The invention relates to an auxiliary drive for utility vehicles having a hydraulic system, such as a drive for the power-take-off shaft of an agricultural tractor, having a friction clutch arranged in the power flow to the power-take-off shaft, and a braking device for the power-take-off shaft, in which the friction clutch and the braking device can be alternately engaged and released.
Used on agricultural tractors, auxiliary drives of this type are known and used as a "rear power-take-off" and "front power-take-off" and are described in U.S. Pat. No. 4,108,291 for example. They are used to drive various work tools used in conjunction with the vehicle and joined to them by means of an articulated shaft. Due to the fact that the available work tools operate at different nominal speeds, the auxiliary drive has a gear system with a corresponding number of gear speeds including a neutral gear, which can be shifted directly on the spot. If the auxiliary drive is not required, the "wet" friction clutch is generally disengaged. In order to prevent rotation of a power-take-off, which may be dangerous, the braking device engages, halting the power-take-off shaft. This being the case, the power-take-off shaft can assume a position in which the articulated shaft of a connecting work tool cannot be linked to the power-take-off shaft or can be so only with great difficulty, and possibly using a technique which is not safe.
One solution for making the power-take-off shaft rotate freely whilst the tool is being assembled is to shift the gear of the auxiliary drive into its neutral position. This solution has already been used in a manner whereby the changeover to neutral position is effected by an appropriate control device when the drive motor of the vehicle is switched off. The disadvantage of this solution, however is that users of such vehicles do not accept a situation in which a gear stage to be engaged after the tool has been assembled has to be shifted manually.